Vershinin stops his soldiers from killing the Doctor and Ace. When the Doctor indicates he knows Sorin's orders, Vershinin takes them prisoner.
As Judson reads the last of the runic translation, new runes etch themselves into the walls of the church. One of the "dead" soldiers in the Viking ship awakes.
The Doctor tells Sorin that he is walking into a trap and that letting them go is the only way to stop whatever is killing his men. He manages to calm the hysterical wounded soldier and finds him clutching a crushed piece of metal. Sorin lets them return to the base.
Judson transcribes the runes and Millington suggests using ULTIMA to decrypt them.
The Doctor and Ace return to the church and inspect the new runes. Hearing noises again, the Doctor looks for a secret entrance but is stopped by Millington emerging from hiding with a gun drawn.
Wainwright, disheartened, preaches to the empty church. The Russian soldiers attack and kill a British patrol.
Millington brings the Doctor and Ace through a laboratory, where a deadly poison is being drawn up from the ground. The Doctor recognizes it as the legendary well of Hvergelmir, an allusion that persuades Millington to show him everything.
They leavie Ace with Wainwright on the way out. Wainwright confesses to Ace that he has lost faith and humanity.
Millington shows the doctor the ULTIMA machine, which he intends to let the Russians steal. Inside it is a vial of poison.
Hardaker, finding out Jean and Phyllis went to Maiden's Point, condemns them as immoral.
Millington shows the Doctor an arsenal filled with poison bombs. He then demonstrates the effectiveness of the poison, using a small sample to kill a crate of doves. The Doctor is appalled. Millington tells him that the ULTIMA will detonate when it tries to decode the word "love".
In the chambers below the church, a green flash blows out a wall of bricks. Soldiers find a sealed flask within but leave it behind.
Jean and Pyllis return to Maiden's Point and frolick in the water in defiance as Hardaker. A mist rolls in over them and the girls vanish.
Millington, hearing the church chambers are cleaned out, orders all transmitters destroyed so that the base is cut off. He also orders all chess sets burnt.
Judson has ULTIMA decrypt the ruins. They read "Let the Chains of Fenric Shatter".
The two girls emerge from the water, transformed. Their hands are claws, their faces pale. They draw a nearby Russian soldier into the water. As he wades out, blue deformed hands reach up and pull him under.
Ace meets with the Doctor and Judson. After the Doctor leaves, Ace realizes that the runes are a logic diagram for a computer. Judson, inspired, has Nurse Crane rush him off to the computer room.
Phyllis and Jean return to the cottage and attack Miss Hardaker. The Doctor and Ace arrive later, to find her dead, completely drained of blood.
The girls next attack Wainwright in the church cemetary. Wainwright tries to hold them off with his Bible, but his lack of faith makes it ineffective. Just before the girls can kill him, the Doctor arrives and forces them to leave.
Millington and Judson work on the computer translation. Millington tells him that all they need is the flask, which glows green in the church basement.
The Doctor is confident of the situation until Ace tells him she revealed the meaning of the runes to Judson.
The ULTIMA machine begins to work at lightning speed and spew out names. As it does, disfigured humanoids, clad in ancient clothing, begin to emerge from the water.
The Doctor races to the ULTIMA room and tries to switch off the power. But Millington tells him he is too late…